Alkylation of hydrocarbons



June 17, 1947.

`F. E. FREY v ALKYLATION HYDROCARBONS Filmadz June 14, 1945 lNvENToR ATTPatented June 17, 1947 ALKYLATION OF HYDROCARBONS Frederick E. Frey,Bartlesville,0kla.,assignor to Phillips Petroleum Company, a corporationof Delaware Application June 14, 1943, Serial No'. 490,808

(Cl. 24W-683.4)

5 Claims.

This invention relates to the catalytic conversion of hydrocarbons. Moreparticularly, it relates to an improved process for alkylatinghydrocarbons in the presence of a catalyst. This application is acontinuation-in-part of my copending application, Serial No. 315,063,led January 22, 1940, now U. S. Patent 2,322,800, issued June 29, 1943.

Many processes have been proposed for alkylating paraiiins with olensand other alkylating reactants, such as an alkyl halide, ether, alcohol,or the like, to produce normally liquid isoparaiiins suitable for use inaviation motor fuel. Several different types of reaction systems havebeen proposed. In my aforementioned copending application, whichdiscloses a hydrouoric acidcatalyzed alkylation process, one of thedisclosed features comprises introducing an olefin multipointwise atsuccessive spaced intervals into a stream comprising a catalyst and analkylatable parain owing through an elongated reaction chamber. I havenow found that this feature has certain important advantages, withrespect to the average or effective composition of the reaction mixtureand the resulting influence on the quality of products, which otherreaction systems do not have. Further, I have found that the heat ofreaction may be readily removed from said elongated reaction chamber bymeans of' a water spray and a current of air applied to its exteriorsurface. Still further, I have yfound that when the parailin and olenreactants for alkylation are initially present in a single mixture,appreciable improvement in quality of products can be obtained byseparating at least part of said reactant paraiiin from said mixture,introducing the separated parain into the inlet end of the elongatedreaction chamber and introducing the remaining olefin-containing mixturemultipointwise at successive intervals spaced along the reactionchamber. Particularly improved results are obtained when the olefin isintroduced so that, as the alkylate content of the reaction mixtureincreases, the ratio of unreacted reactant paraiiin to olefin isincreased. This feature applies in the use of other alkylating`catalysts also, such as sulfuric acid, ohlorosulfronic acid, phosphoricacid, Friedel-Crafts catalysts, etc.

An object of the present invention is to provide an improved process forcarrying out catalytic alkylations of hydrocarbons. A specic object .isto provide an eicient means for removing exothermic heat of reaction.Another specic object is to increase the effective ratio of reactantvhydrocarbon to product hydrocarbon in the action zone, whereby theproportion of surviving primary reaction products is increased. Other`objects and advantages of the invention will be apparent from theaccompanying description and discussion.

Inv all alkylation systems, the following three maj or conditions mustbe met in order to produce av high-quality product. (1) Theconcentration of olefin (or other alkylating reactant) throughout 'thereaction mixture must be maintained sumciently vlow that polymerizationor other `olefinoleiin reactions donot occur to an appreciable extent incomparison with alkylation (olenparain reactions). (2) The concentrationof product in the reaction mixture must be maintained sufficiently lowrelative to the concentration of reactants that secondary reactions(degradation of the primary reaction. products) do not occur to anappreciable extent in comparison with primary reactions. (3) Thereaction temperature must be maintained at such a value that thevelocity constants of primary reactions are optimum in relation to thevelocity constants of side and secondary reactions.

Condition 1 may be satisfied in practice in several Ways. For example,the reaction mixture may be circulated rapidly, either externally to thereaction zone or internally, past one or more inlets through whicholefin is introduced at a rate sufficiently low that it is consumed byalkylation before its concentration can build up to a value such thatappreciable polymerization can occur. The olefin may be introducedmultipointwise kinto an elongated reaction zone through which thereaction mixture flows, the distance between successive olen inletsbeing sufficient to allow most of the olefin introduced at one point tobe consumed by alkylation before the reaction mixture passes the nextolefin inlet. It appears that, for optimum results in the alkylation ofisobutane with an olefin having three to five carbon atoms per molecule,the maximum concentration of unreacted olefin in the reaction mixtureshould always be below about 5 mol per cent of the isobutane and usuallywell below l mol per cent. (By unreacted olefin is meant simpleolefincatalyst complexes as well as free oleiin.) In alkylations withethylene, somewhat higher concentrations of olefin are permissible. Itshould be understood that the maximum allowable concentration of olefin(or other alkylating reactant) varies appreciably with specic propertiesof the alkylatable hydrocarbon and the catalyst, and with temperature,and that it is extremely di- ,cult to measure directly or even toestimate the olefin concentration accurately in catalytic systems.Although in practice the concentration of olefin is automatically xed byother variables such as reaction time, temperature, nature of catalyst,and nature of reactants, it is of interest to the present discussionbecause it -is a fundamental variable which maybe used in derivingequations suitable for correlating experimental data and for designpurposes, as will be discussed hereinafter.

Condition 2 is usually satisfied in practice by feeding a considerableexcess of reactant-parafn to the reaction zone. It appears that whencondition 1 is satisfied the composition of the product may besatisfactorily correlated with the effective ratio of reactant-paraiiinto product in the reaction zone by an equation of the following form:

AWhere P is the volume per cent of primary reaction products in thetotalproducts, I/A is the elective mol ratio of reactant-paraffin tototal product in the reaction mixture, and 7c is a constant vWhichdepends upon reaction temperature, specific properties of the reactants,and specic Yproperties and condition of the catalyst. Theoretically, lcrepresentsthe ratio of the average Avelocity'constant for secondaryreactions of the first-'formed or primary reaction products to theaverage velocity constant for formation of the primary products.

For a reactionv system in which the reaction mixture is circulatedrapidly past one or more `feed inlets, the ratio of reactant-paralnn toproduct is substantially constant throughout the reaction zone and isequal to that in the total effluents from the reaction zone. As anapproximation, found to be valid under reasonably good alkylationconditions under which approximately theoretical yields are obtained,the mol ratio of reactant-paraffin to product in such a circulation`system may be said. to be one less than the ,over-fall mol ratio ofreactant-paran to ol'en in the feed to the reaction Zone, includingrecycled, unreacted, reactant-parain. That is: (2i) I/A=I/O-1 Where I/Ois the over-all mol ratio of reactant- Y paraffin to olefin in the feedto the reaction zone.

For a single-pass reaction system in which an olefinicstream isintroduced at successive inletsv in such a reaction system may beexpressed in terms of the vfeed composition as follows:

Y Y YI/A='2I/O-J/O1 where J/O is the Vmol ratio of reactant-paraffin to,olefinji-n the volelinic stream Which is introducedV.multijjioin'tvvise. l

@From a comparison of Equations 2 and 3, it

follows thatfor a given over-all feed in which at least -part of thereactant-paraffin is separate Vfrom `the olen, a higher eiective ratioof reactant-paraffin to product in the reaction zone is .obtainable .ina single-pass system with multipointwise introduction of olen than in af1'@- circulation system. Furthermore, it follows that for a single-passmultipoint system having a feed in which the reactant-parain and olefinare present in a single stream, an appreciable and advantageous increasein the effective ratio vci reactant-paraffin to product in the reactionzone can be gained by separating at least part of the reactant-parafiinfrom the total feed, introducing this separated part into the rst partof the reaction zone andv introducing the remaining olefin-containingpart into the reaction zone at successive spaced intervals.

In addition, most of the undesired secondary react-ions Ibetween thealkylate and the reactants involveprmarily the alkylating reactant (suchas the olens) rather than the reactant-parailin, and I have found that abetterrproduct results in asingle-'pass system when the ratio ofreactant-paraiin to alkylating reactant is substantially higher in thelatter part of the reaction zone than inthe first part of the Zone.Thus, in accordance with -the present invention, kI 'nd that increasedyields per pass with high quality of valkylate result from single-passoperation, without recirculation ofthe reaction mixture or of theeiluent hydrocarbon mixture, when this operation is conducted Withintimate mixing of reactants and catalyst, With addition of alkylatingreactant at a plurality of points along an elongated reaction` Zone,with a, mol ratio of reactant-parafnn to alkylating reactant of about10:1 or more at the inlet of the reaction zone and with successivelyhigher ratios of these reactants at subsequentpoints of addition of thealkylating reactant, thel highest ratio being v:1 or more. As comparedwith a recirculation-type process, the yields( of alkylate and the`quality of the alkylate are higher lWhen practicing my invention thanwith even higher ratios of reactantparaiiin to alkylating reactant inthe recirculation-type process and, of course, the equipment is muchsmaller per unit volume of alkylate produced. It is also desirable, -inthe practice of my invention, to limit the amount of alkylate, in thefinalV effluent of the reaction zone, to about 30 per cent by Weight ofthe total hydrocarbons.

Condition' 3, relative to maintenance of: an

optimum' reaction temperature, requires the strikingof a balance amongseveral factors whichvary with speciic properties of reactants andcatalysts. In general, the over-al1 velocity constant for polymerizationand similar side reactions of olens appears to be about as high orhigher, and to have a lower temperature coefficient, than that `foralkylation; hence, increasing the reaction temperature tends to increasethe rate of alkylation relative to polymerization in the reactionmixture, provided that condition 1 (satisfactorily low-olefinconcentration) is satisfied. Since there is vnecessarily a relativelyhigh momentary local `concentration of olen at the point of introductionof olefin, condition 1 is 'somewhat harder to satisfy at the highertemperatures. That is, an increase inr temperature makes it necessary todisperse the incoming olen with Vincreased rapidity in order to prevent.appreciable polymerization resulting from high local concentrations ofolen at the olenn inlets.u

VrI he over-all velocity constant fordegradation 'of the primaryproducts by secondary re'- actions 'such' as secondary allikyla'tion,reconstruction,z isomerization, or the' like Vappears vto be slightlyhigher and to have a higher temperature coeicient than the constant forprimary alkylation, Hence -to minimize degradation of primary alkylate,it is desirable to maintain as low a reaction temperature as possiblewithout unduly extending the required reaction time, or without causingexcessive polymerization of the olen.

One especially advantageous mode of alkylation employing multipointwiseaddition of olefin at successive spaced inlets along an elongatedreaction zone comprises correlating the rate of olefin introduction withthe cross-sectional area of the reaction zone and with the velocity offlow along the reaction zone at each particular olefin inlet in such away that this rate is progressively decreased in the direction of iiowin correspondence with the increase in the local concentration of inerts(hydrocarbons other ythan reactant or alkylatable hydrocarbon) caused byremoval of alkylatable hydrocarbon through reaction with the olefin,whereby the concentration of unreacted olefin decreases and the ratio ofreactant paraiin to olen increases.

An understanding of some aspects of the invention may be aided byreferences to the accompafnying drawing which is a schematic flowdiagram of a preferred arrangement of apparatus for practicing theinvention. Although for the sake of brevity and specific illustrationthe following discussion is concerned principally with the alkylation ofisobutane with b-utylenes 'in the presence of concentrated hydrofluoricacid, the invention is applicable to many other alkylations and shouldnot be limited unduly by mention of specic reagents, apparatus,catalysts, or conditions.

A C4 fraction of refinery gases' comprising isobutane, normal butane,and butylenes may be admitted through inlet I to fractionator li,Whereingit is separated into an isobutane-rich fraction and abutylene-rich fraction. Preferablythis fractionation is so conductedthat only a minor amount of oleiins is included with the isobutane. Theisobutane-rich fraction, which with optional additional isobutaneadmitted through inlet I2 and/or recycle conduit I3 preferablycontainsrnot more than about 2 mol per cent of oleiins, is passed inliquid phase through conduit I4 to pump I5 whereby it is thoroughlymixed with liquid concentrated hydroflucric acid, which may be admittedthrough inlet I6, and is forced through reaction coil II. Thebutylene-rich fraction from fractionator II is forced by pump I8 througha plurality of jet inlets, such as at I9, 2li, 2|, and 22, into reactioncoil I'I. If desired, or expedient, the sole charge to the process maybe isobutane through conduit I2 and an olefin-containing fractionthrough conduit 48.

Reaction coil I'I preferably comprises a number of lengths of steel pipejoined by U-bends at the ends to form a single continuous reaction tube.AThe coil should be so dimensioned that How of fluid through it isturbulent; the linear velocity may be from about 2 to 8 feet per secondor more, depending somewhat upon the size of the pipe. However, in orderto obtain and maintain intimate and thorough mixing, or emulsiflcation,of the liquid hydroiluoric acid and liquid hydrocarbon material a rateof flow greater than that which will just give turbulent How isgenerally desirable, and such a rate may be as high as 50 or 100- feetper second, or more. As the rates of flow increase the power costs foroperating the pump I increase materially, and in any speciccase it willbe necessary to strike a suitable balance between improved alkylationVmined by one skilled in the art, in the light of the present disclosureand discussion. Olen inlet jets may be conveniently located at theU-bends, and for hydrofluoric acid alkylations may be designed tooperate with a pressure drop of about 50 to 500 pounds per square inch.In general, the pressure drop across the olefin inlet jets should besuiiicent to disperse the olefin rapidly and uniformly throughout thelreaction stream. Preferably the rate of oleiin introduction at any jetis not more than about 2 mol per cent of the rate of iiow of isobutanepast the jet i. e. a mol ratio of isobutane to'olen of at least about50:1; at higher rates of olefin introduction, polymerization at theolefin inlet tends to become excessive, owing to high localconcentrations of olen. The reaction coil, if horizontal, may bearranged so that the reaction mixture flows upward around most of theU-bends in order to minimize the tendency for hydrofluoric acid tosettle to the bottom of the conduit. However, if the reaction coil isarranged with the straight sections positioned vertically this tendencyis eliminated. In a. Vertical coil the hydrouoric acid and hydrocarbonphases may be maintained in a state of intimate mixture simply bymaintaining turbulent flow conditions or a linear velocity greater thanthe velocity of settling or stratification. Thus a lower linear velocityand a correspondingly shorter coil may be used if the coil is positionedvertically than if it is positioned horizontally.

In a preferred modification, the pipes of the reaction coil are spacedseveral inches apart, wooden vslats (not shown) are supported in thespaces, Water is introduced through conduit 50 and pump 5I and issprayed on the top of the coil, and a current of air is blown by fan 52through the coil externally to the pipes, thereby effecting rapidremoval of the heat of reaction and permitting a desired reactiontemperature to be readily maintained. Preferably a corrosion inhibitoris added to the spray water and/or the exterior surfaces of the reactioncoil are painted or otherwise treated to minimize corrosion. Paintingreduces the cooling eiciency somewhat but usually the resultingdecrease, in corrosion will more than offset such a minor loss incooling eiciency.

From reaction coil II, the reaction mixture or stream is passed toseparator 23 where it is separated into a liquid hydrocarbon phase and aliquid hydrofluoric acid phase. The .denser or hydroiiuoric acid phaseis withdrawn through pipe 24 and may be returned to the reaction systemthrough valve 25 and pipe 26. Generally a substantial portion of theacid is so recycled. If desired, the hydrouoric acid may be withdrawnthrough valve 21 andpipe 28 to acid-recovery system 29, where theacid-soluble materials and any water which may be present are removed.After this treatment, the acid may be returned to the reaction systemthrough valve 30 and pipe 3|, and the tar andy water may be Withdrawn,as through outlet 32 controlled by valve 33.

The hydrocarbon phase including dissolved hydrofluoric acid, is Apassedfrom separator 23 through valve 34 and conduit 35 to deisobutanizer 35.The unconverted or unreacted isobutane, associated with thisdissolvedhydro'uoric acid, is recycled through valve 3'I and conduit I3 to thereaction coil. Any portion or all of this stream may be dischargedthrough conduit 4l forzseparation of VVlight gases,fsuch vaspropaneetc., .which `may b e present in the charge and/or u:may be formed insmall amountsby side reactions. The visobutane-free allsylate is'removedfrom vthe Vkettle of the,deisobutanizerthrough vvalve 38-andconduit'3-9 to deb-utanizer 110, where the normal butane is removedthrough outlet 4l. The fbutane-free alkylate is -passed through valveYl2 4and conduit 43 to rerun .column lill, in which it fis fractionated-into a motor-.fuel fractionfanda heavy or oil lfraction; it ,also maybe :subjected .to any other treatment, -such las'caustic Washing,fractionation, and the like, as may `be desired or necessary. Theymotor-fuel fraction is Withzdrawn as a product 'through outlet 7.45,and vthe oil rfraction through outlet '46.

It will be understood 'that the viloW diagram .is schematic only, andth-at many additional .pieces of equipment, such as pressure gauges,

zacid. The residual `or' butylene-*normal .bu-tane `decreased in thedirectionof flow not only .to

counterbalance the effect kof the decrease .in-isobutane concentrationcaused byconsumption'to .form the alkylate but also to counterbalancethe effectof the increase in the local concentration of inerts in thereactionrstream, as isshownby the data in the .following tabulation, andto counterbalance the increased concentrationso alkylate. Y

YMols Addition Point Olen Isobutane/ -Alkylate after Composition afterreaction,

olefin at added .addition Y. n 04H10 point 04H10 H CAHI Alkylatereaction Entrance 1 1 Includes 2.2 mols in isobutane stream.

owmeters, pumps, heat exchangers, reflux accumulators, reflux lines, andthe like, will be necessary in any particular -installation and can .be'installed by anyone skilled in the art. However, the essentialequipment and material flows `have been described i-n sufficient detailto serve .as an efficient guide. When using :a solid catalyst, it may besuspended -in a reaction mixture, to form a slurry, or it may be used ina lon-g bed, or in a series of beds which together will comprise a`single reaction zone, 'with suitable removal of heat, and with additionof olen along the length ofthe reaction zone in `the manner disclosedand discussed herein.

To illustrate further some aspects of -my invention, .the followingexample is given.

IA `liquefied -butane-butylene fraction `of re- Arlnery gases comprisingisobutane and butylenes in a mol ratio of 3 to '1 and some Ynormalbutane yis introduced to a hydrofiuoric acid alkylation system similarto that illustrated in the drawing. Most of the -isobutane is separatedfrom the mix-- `ture by fractionation as an olefin-poor overhead Vstream, giving a residue or kettle stream rich in olefin; thecompositions of these streams are as follows:

The isobutane-rich, or overhead, fraction from the fractionation isintroduced into the inlet end of the reaction coil with hydrouoric acidvto give a mixture having 44 percent by volume hydrocarbon and 56 percent by volume hydrofluoric .ing material or heavy alkylate.

The temperature in the reaction coil is .maintained at about F. by meansof a circulating water spray and a forced draft of air applied to theexterior surface of the reaction coil. The efiluent from the reactioncoil is allowed tosettle; most of the resulting BIF layer is recycled tothe inlet of the reaction coil, and part is passed to acid-regenerationmeans for purification. The hydrocarbon layer from the settling step .isdebutanized, and the alkylate is fractionated to remove a smallproportion of relatively 4highfboil- The resulting gasoline-rangealkylate has a clear A. S. T. -M. octane number of 90.9. For comparison,passing the same feed directly to the `reaction coil instead of rstseparating it into an isobutane-rich yfraction and a butylene-normalbutane fraction results in an A. S. T. M. octane number of y88.4. At atemperature of 75 F., the octane number of the gasoline product fromalkylation Yby .the special multipoint addition of olefin-rich Yfractionis 92.5, whereas passing the feed directly tothe reaction coil givesonly 90.4. These data Vshovv that considerable improvement in thequalityof the hydrofluoric acid alkylation Vproduct is affected byfeeding the reactant paraffin-rich stream separately from the olefins inthe manner described hereinbefore. l

The invention may be practicedotherwise than as specifically shown, andmany variations and modifications of it will be apparent to thoseskilled in the art in the light of the present disclosure anddiscussion.

I claim:

1. An improved process for reacting by catalytic alkylation butylenesand isobutane contained in an olefin-containing C4 hydrocarbon mixtureto produce parafilns of higher molecular weight, whichcomprisessubjecting such a mixture to fractional distillation andrecovering as av low-boiling fraction a fraction rich in isobutane andcontaning no more than a minor proportion of the olens in the originalmixture and as a high-boiling fraction a fraction containing no morethan a minor amount of isobutane and a major proportion of the olefns inthe original mixture, passing said low-boiling fraction in admixturewith liquid hydrofluoric acid to one end of an elongated alkylation zonecomprising a series of horizontal pipes in a vertical row joined at theends to form a continuous upwardly rising coil, adding said mixture atthe bottom of said coil and flowing said mixture upwardly through saidcoil at a ilow rate such that intimate admixture of liquid hydroluoricacid and liquid hydrocarbons is maintained, adding portions of saidhigh-boiling fraction at successive points along the length of saidreaction zone in amounts such that the mol ratio of isobutane, in themixture at the first point of addition, to olefin in the portion addedat said first point is at least 50:1 and such that the mol ratio ofunreacted isobutane in the mixture to olefin added at each successivepoint is progressively higher, spraying Water over the outside of saidcoil and forcing air over the outside of said coil generally concurrectto the ilow of reactants through said coil and countercurrent to theflow of said sprayed water, withdrawing the resulting reaction mixturefrom the top of lsaid coil and recovering therefrom a fractioncomprising paraiiins of higher molecular weight so produced.

2. In a process for catalytically alkylating an alkylatable hydrocarbonin an elongated reaction Zone of the pipe-coal type at a reactiontemperature near atmospheric, the improvement which comprises passing anintimate liquid mixture of an alkylatable hydrocarbon and liquidalkylation catalyst to a pipe coil comprising a series of horizontalpipes in a vertical row joined at the ends to form a continuous upwardlyrising coil, adding said mixture at the bottom of said coil and ilowingsaid mixture upwardly through said coil at a rate of at least 2 feet asecond and suflicient to obtain and maintain intimate and thoroughmixing of said liquid hydrocarbons and of said liquid catalyst, addingan olefin-containing material at a series of points along the length ofsaid coil in an amount at each said point such that the ratio ofunreacted alkylatable hydrocarbon to unreacted olefin is progressivelyhigher at successive points in the direction of flow of said mixture,spraying water over the outside of said coil, forcing air over theoutside of said coil generally countercurrent to the flow of reactantsthrough said coil and countercurrent to the flow of said sprayed water,passing the resulting reaction mixture from the top of said coil andrecovering therefrom an alkylate fraction so produced.

3. In a process for catalytically alkylating an 10 alkylatablehydrocarbon in an elongated reaction Zone of the pipe-coil type at areaction tempera` ture near atmospheric, the improvement which comprisespassing an intimate liquid mixture of an alkylatable hydrocarbon andliquid alkylation catalyst to a pipe coil comprising a series ofhorizontal pipes in a vertical row joined at the ends to form acontinuous upwardly rising coil, adding said mixture at the bottom ofsaid coil and flowing said mixture upwardly through said coil at a rateof at least 2 feet a second and suflicient to obtain andmaintainintimate and thorough mixing of said liquid hydrocarbons and of saidliquid catalyst, adding an olefin-containing material at a series ofpoints along the length of said coil, spraying water over the outside ofsaid coil, forcing air over the outside of said coil generallyconcurrent to the W of reactants through said coil and countercurrent tothe flow of said sprayed Water, passing the resulting reaction mixturefrom the top of said coil and recovering therefrom an alkylate fractionso produced.

4. The process of claim 2 in which said alkyatable hydrocarbon is alow-boiling isoparafn and said liquid alkylation catalyst ishydrofluoric acid.

5. The process of claim 3 in which said alkylatable hydrocarbon is alow-boiling isoparaiiin and said liquid alkylation catalyst ishydrofluoric acid.

FREDERICK E. FREY.

REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATE-N TS Number Name Date 2,002,394 Frey May 21, 19352,246,703 Thiele June 24, 1941 2,260,990 Goldsby Oct. 28, 1941 2,267,730Grosse Dec. 30, 1941 2,273,041 Ipatieif Feb. 17, 1942 2,311,096 StrawnFeb. 16, 1943 2,314,435 Allender Mar. 23, 1943 2,322,800 Frey June 29,1943 2,325,052 Grosse July 27, 1943 849,944 Heuvel Apr. 9, 19072,327,926 Oakley Aug. 24, 1943 2,332,564 Egloif Oct. 26, 1943 2,335,704Smith Nov. 30, 1943 2,357,607 Ocon Sept. 5, 1944 2,370,771 Bowerman Mar.6, 1945 FOREIGN PATENTS Number Country Date Great Britain July 29, 1941

